1. Field of the Invention
The present invention relates to an optical head device for recording information to, or reproducing or erasing information from, an information memory medium, for example, an optical disk or optical card. The present invention also relates to an optical information processing apparatus, and an inclination angle detection apparatus for detecting an angle made by a beam collected by a light collection system in an optical information processing apparatus and an information memory medium.
2. Description of the Related Art
Optical memory technologies which use optical disks or optical cards as high density, large capacity memory media are used in progressively wider fields, for example, in digital audio disks, video disks, document file disks and data files. By such optical memory technologies, information is recorded to, or reproduced from, an optical disk with sufficiently high precision and satisfactory reliability through a light beam which is focused to have a microscopic diameter. The performance of a recording and reproduction apparatus using the optical memory technologies significantly relies on the optical system.
Exemplary basic functions of the optical head device, which is a main part of the optical system, are rough classified into:
(1) light collection in order to form a smallest possible light spot only limited by the diffraction;
(2) focusing and tracking control of the optical system, and reproduction of information signals; and
(3) erasing and writing of information signals by collected light.
These functions are realized by a combination of various optical systems and a light detector of a photoelectric conversion system.
As a first conventional example comparative to the present invention, a conventional optical head device will be described with reference to FIG. 42. FIG. 42 is a schematic view of an optical system of the conventional optical head device. In the optical head device shown in FIG. 42, focusing is performed by the non-point aberration method and tracking is performed by the push-pull method and the phase contrasting method.
The optical head device shown in FIG. 42 operates in the following manner.
Light emitted by a semiconductor laser 101 as a light source is reflected by a plane-parallel beam splitter 102 and collimated by a collimator lens 103, which is included in a light collection system. The light is then collected by an objective lens 104 which is also included in the light collection system, and collected on an information layer 108 of an optical disk 105, which is an information memory medium. An actuator 107 moves the objective lens 104 and a holding device 106 in accordance with fluctuations or decentration of the optical disk 105.
The light is then diffracted and reflected by the information layer 108 of the optical disk 105 to be reflected light 108a. The reflected light 108a is converged by the collimator lens 103. The reflected light 108a is then provided with an non-point aberration when passing through the plane-parallel beam splitter 102. The light provided with the non-point aberration is received by a light detector 150. The above-described elements in the optical system shown in FIG. 42 are arranged so that, when a focal point F0 of the light from the objective lens 104 is on the information layer 108, a light detecting surface of the light detector 150 is in the least circle of confusion of the converged light provided with the non-point aberration.
FIG. 43A shows a pattern of a light detection area of the light detector 150 and the shape of a cross section of the reflected light 108a detected by the light detector 150. The light detector 150 includes four light detection areas 251 through 254. Signals obtained in accordance with the amount of light received by the light detection areas 251 through 254 are referred to herein as s1 through s4. Although an operation circuit for generating a tracking error signal is not shown, a tracking error signal TE1 is generated according to expression (1).
TE1=(s1+s4)xe2x88x92(s2+s3)xe2x80x83xe2x80x83(1) 
By the phase contrasting method, a tracking error signal TE2 is obtained by comparing the phase of a sum signal of s1 and s3 and the phase of a sum signal of s2 and s4.
A focusing error FE signal by the non-point aberration method is generated according to expression (2).
FE=(s1+s3)xe2x88x92(s2+s4)xe2x80x83xe2x80x83(2) 
When the information layer 108 of the optical disk 105 is distanced from the objective lens 104 so as to be beyond the focal point F0 of the light from the objective lens 104, the cross section of the reflected light 108a detected by the light detector 150 is as shown in FIG. 43B. When the information layer 108 of the optical disk 105 approaches the objective lens 104 so as to be between the objective lens 104 and the focal point F0 of the light from the objective lens 104, the cross section of the reflected light 108a detected b the light detector 150 is as shown in FIG. 43C.
An RF signal, which is an information reproduction signal, is a sum of the signals s1 through s4 obtained from all the light detection areas and thus is generated according to expression (3).
RF=s1+s2+s3+s4xe2x80x83xe2x80x83(3) 
The conventional optical head device described above have the following problems.
(1) The tracking error signal is generated by a differential signal which indicates the difference between the signals respectively obtained from the two light detection areas defined by simply equally dividing the light detection surface (aperture) of the light detector 150 into two by a central line of the aperture. In such a structure, the light is incident off the track or tracking is not stably controlled when an aberration occurs due to an inclination of the objective lens 104 and/or the optical disk 105 (tilt), or when the objective lens moves in a direction perpendicular to the tracks with respect to the optical axis in accordance with the decentration of the optical disk 105.
(2) When the focal point of the light from the objective lens 104 scans the position off the track in which the information to be reproduced is stored, if a reproduction signal is generated by a signal indicating the difference between the signals respectively obtained from the two light detection areas defined by simply equally dividing the aperture of the light detector 150 into two by a central line of the aperture, a sufficient margin with respect to the disturbance cannot be secured.
Regarding an inclination angle detection apparatus for detecting an inclination of a beam collected by a light collection system in an optical information processing apparatus with respect to the information memory device, various structures have been proposed in order to accurately read information from, and write information to, the information memory device.
As a second conventional example comparative to the present invention, a conventional inclination detection apparatus will be described with reference to FIG. 44. FIG. 44 is a schematic view of an inclination detection apparatus. The inclination detection apparatus shown in FIG. 44 operates in the following manner.
A linearly polarized scattering beam 70 emitted from a semiconductor laser 101 as a light source is collimated by a collimator lens 103 and then is incident on a polarizing beam splitter 130. Next, the beam 70 is transmitted through the polarizing beam splitter 130 and then through a xc2xc-wave plate 122 to be converted into a circularly polarized beam. The circularly polarized beam is collected on an optical disk 105 as an information memory medium by an objective lens 104.
FIG. 45 shows a structure of the optical disk 105. In FIG. 45, Gnxe2x88x921, Gn, Gn+1, . . . each represent a guide groove. Information is stored in the guide grooves as a mark or a space. Accordingly, tracks Tnxe2x88x921, Tn, Tn+1, . . . for storing information correspond to the guide grooves Gnxe2x88x921, Gn, Gn+1, . . . Also in FIG. 45, Gp represents a space between two adjacent guiding grooves (i.e., cycle of the grooves) and tp represents a space between two adjacent tracks (i.e., cycle of the tracks). The values of Gp and tp are equal to each other.
The beam 70 which is reflected and diffracted by the optical disk 105 is again transmitted through the objective lens 104 and then through the xc2xc-wave plate 122 to be converted into a linearly polarized beam which runs in a direction perpendicular to the direction of the light emitted from the semiconductor laser 101. The beam 70 is then entirely reflected by the polarizing beam splitter 130 and converted into a converged beam (still indicated by reference numeral 70) by a detection lens 133. The converged beam 70 is transmitted to the planar polarizing plate 134 and received by a light detector 158. The beam 70 is provided with a non-point aberration for focusing error detection when passing through the planar polarizing plate 14. The beam 70 received by the light detector 158 is converted into an electric signal in accordance with the light amount thereof.
In this specification, in the case where the optical disk is a ROM disk, a mark indicates a pit, and a space indicates a plane part. In the case where the optical disk indicates a phase-change memory medium, a mark indicates an amorphous portion and a space indicates a crystal portion, or a mark indicates a crystal portion and a space indicates an amorphous portion. In the case where the optical disk is a magnetic memory medium, a mark indicates an upward magnetization and a space indicates a downward magnetization, or a mark indicates a downward magnetization and a space indicates an upward magnetization. Alternatively, in the case where the optical disk is a magnetic memory medium, a mark may indicate a rightward magnetization and a space may indicate a leftward magnetization, or a mark may indicate a leftward magnetization and a space may indicate a rightward magnetization. In the case where the optical disk is a write-once disk such as a CD-R, a mark indicates a dye burned area and a space indicates a non dye burned area.
The focusing error signal and the tracking error signal are each added to the actuator 107. The position of the objective lens 104 is adjusted so that the beam 70 emitted by the light source 101 is focused at a desired position on the optical disk 105. The methods for generating a focusing error signal and a tracking error signal are well known and thus will not be described here.
FIG. 46 shows a signal processing section 703 including the light detector 158. The electric signal from the light detector 158 is input to the signal processing section 703. As shown in FIG. 46, the light detector 158 includes four light detection sections 158A, 158B, 158C and 158D. The signals from the light detection sections 158A through 158D are respectively current/voltage converted by current/voltage converters 855 through 858. The signals from the current/voltage converters 855 through 858 are sent to an operation section 871 for a differential operation. The signal from the operation section 871 is output from a terminal 814. The signal from the terminal 814 is an inclination detection signal.
In the case where an inclination is detected by the above-described conventional inclination detection apparatus utilizing that eclipse of the beam 70 reflected by the optical disk 105 occurs by the aperture diaphragm of the objective lens 104, the detection sensitivity reduces as the numerical aperture of the objective lens 104 increases. Recently, a structure has been proposed in which the numerical aperture of the light collection system is 0.6 and the thickness of the information memory medium is 0.6 mm in order to increase the information which can be stored in one information memory medium. In such a structure, a mere about 0.5 degree change in the angle made by the beam collected by the objective lens and the information memory medium significantly changes the jitter characteristics of the information read from the information memory medium. In the case where an inclination servo for compensating for the change in the angle made by the beam collected by the objective lens is introduced, the inclination detection apparatus needs to detect the inclination with an error of 0.5 degrees or less. However, in the conventional inclination detection apparatus, when the numerical aperture of the objective lens is 0.6, even if the inclination is actually, for, example, 0.5 degrees, the inclination detection signal changes only by about 2%. Thus, it is difficult to precisely detect the inclination of 0.5 degrees or less.
As a third example comparative to the present invention, another conventional optical head device will be described with reference to FIG. 47.
A linearly polarized scattering beam 70 emitted by a semiconductor laser 101 as a light source is collimated by a collimator lens 103 and then is incident on a polarizing beam splitter 130. The beam 70 is transmitted through the polarizing beam splitter 130 and then through a xc2xc-wave plate 122 to be converted into a circularly polarized beam. The circularly polarized beam is collected on an optical disk 105 by an objective lens 104. The beam 70 reflected and diffracted by the optical disk 105 is again transmitted through the objective lens 104 and then through the xc2xc-wave plate 122 to be converted into a linearly polarized beam which travels in a direction perpendicular to the direction of the light emitted from the semiconductor laser 101. The beam 70 is then entirely reflected by the polarizing beam splitter 130 and converted into a converged beam (still indicated by reference numeral 70) by a detection lens 133. The converged beam 70 is transmitted to the planar polarizing plate 134 and received by a light detector 158. The beam 70 is provided with a non-point aberration for focusing error detection when passing through the planar polarizing plate 134. The beam 70 received by the light detector 158 is converted into an electric signal in accordance with the light amount thereof.
FIG. 48 shows a signal processing section 705 including the light detector 158. The electric signal from the light detector 158 is input to the signal processing section 705. As shown in FIG. 48, the light detector 158 includes four light detection sections 158A, 158B, 158C and 158D. The signals from the light detection sections 158A through 158D are respectively current/voltage converted by current/voltage converters 851 through 854. The signals from the current/voltage converters 851 and 854 are added together by an addition section 891, the signals from the current/voltage converters 852 and 853 are added together by an addition section 892, the signals from the current/voltage converters 851 and 853 are added together by an addition section 893, and the signals from the current/voltage converters 852 and 854 are added together by an addition section 844. The signals from the adding sections 891 and 892 are sent to an operation section 871 for a differential operation, and the signals from the adding sections 893 and 894 are sent to an operation section 872 for a differential operation. The signal from the operation section 871 is output from a terminal 811, and the signal from the operation section 872 is output from a terminal 812. The signal output from the terminal 811 is a tracking error signal, and the signal output from the terminal 812 is a focusing error signal. The focusing error signal is generated by a well known method referred to as the xe2x80x9cnon-point aberration methodxe2x80x9d, and the tracking error signal is generated by a well known method referred to as the xe2x80x9cpush-pullxe2x80x9d method. The focusing error signal and the tracking error signal are respectively added to an actuator 107 for focusing control and another actuator 107 for tracking control. The position of the objective lens 104 is adjusted so that the beam 70 from the semiconductor laser 101 is focused at a desirable position on the optical disk 105.
FIG. 49 shows a structure of the optical disk 105 (FIG. 47). In FIG. 49, Gnxe2x88x921, Gn, Gn+1, . . . each represent a guide groove for allowing tracking error signal detection. Information is stored in and between the guide grooves as a mark or a space, where a space between two adjacent guiding grooves is Gp and a space between two adjacent tracks is tp, Gp=2xc2x7tp.
In the optical head device described as the third example, the following conditions, for example, are adopted in order to store a great amount of information in the optical disk 105. The wavelength xcex of the beam 70 from the semiconductor laser 101 as the light source is 650 nm, the numerical aperture NA of the objective lens 104 is 0.6, the thickness t of the optical disk 105 is 0.6 mm, the distance Gp between centers of two adjacent guiding grooves is 1.48 xcexcm, and the distance tp between centers of two adjacent tracks is 0.74 xcexcm. When the angle made by the beam 70 collected by the objective lens 104 and the optical disk 105 is a proper angle, the tracking error signal zero-crosses when the center of the guiding groove is irradiated by the beam 70 collected by the objective lens 104. However, when the angle made by the beam 70 collected by the objective lens 104 and the optical disk 105 is not a proper angle, the tracking error signal does not zero-cross when the center of the guiding groove is irradiated by the beam 70 collected by the objective lens 104. At this point, the tracking error signal is hardly offset but is phase-shifted. Such a phase shift can be a cause of an off-track. For example, when the phase shift is about 0.5 degrees, a 0.1 xcexcm off-track is caused. When the off-track is caused, the information stored in the optical disk cannot be accurately read or erased.
According to one aspect of the invention, an optical head device includes a light source for emitting at least one of a coherent beam and a quasi-monochromatic beam; a collection optical system for collecting the beam emitted by the light source to an information memory medium having a track which has at least one mark and at least one space; a light detector having a plurality of detection areas for receiving the beam reflected by the information memory medium and outputting a signal in accordance with a light amount of the beam received; and a tracking error signal generator for receiving the signals output from the light detector and generating a tracking error signal based on the signals. The tracking error signal generator reduces a difference between a first signal amplitude and a second signal amplitude. The first signal amplitude is an absolute value of a difference between a first signal level and a second signal level. The second signal amplitude is an absolute value of a difference between the first signal level and a third signal level. The first signal level is a value of the tracking error signal obtained when the beam emitted by the light source is radiated to a center of the track. The second signal level is a maximum value of the tracking error signal obtained when the information memory medium is scanned by the beam emitted by the light source in a direction perpendicular to the track. The third signal level is a minimum value of the tracking error signal obtained when the information memory medium is scanned by the beam emitted by the light source in a direction perpendicular to the track.
According to another aspect of the invention, an optical head device includes a light source for emitting at least one of a coherent beam and a quasi-monochromatic beam; a collection optical system for collecting the beam emitted by the light source to an information memory medium having at least one track, at least one mark and at least one space; a light detector having a plurality of detection areas for receiving the beam reflected by the information memory medium and outputting a signal in accordance with a light amount of the beam received; a tracking error signal generator for receiving the signals output from the light detector and generating a tracking error signal based on the signals. The tracking error generator subtracts, from the tracking error signal, a component of the signal obtained from an overlapping area. In the case where an aperture of the collection optical system is a circle having a radius of 1, the overlapping area is an area where two circles overlap, the circles each having a radius of 1 and being centered around a point which is xcex/(NAxc2x7Gp) away, in a direction perpendicular to the track, from a center of the aperture, where xcex is the wavelength of the beam emitted by the light source, NA is the numerical aperture of the collection optical system, Gp is the distance between centers of two adjacent tracks of the information memory medium, and xcex/(NAxc2x7Gp) less than 1.
According to still another aspect of the invention, an optical head device includes a light source for emitting at least one of a coherent beam and a quasi-monochromatic beam; a collection optical system for collecting the beam emitted by the light source to an information memory medium having at least one track, at least one mark and at least one space; a light detector having a plurality of detection areas for receiving the beam reflected by the information memory medium and outputting a signal in accordance with a light amount of the beam received; a tracking error signal generator for receiving the signals output from the light detector and generating a tracking error signal based on the signals; and a light division element for dividing an overlapping area of the reflected beam and the vicinity thereof so as to be received by the light detector. The vicinity of the overlapping area refers to an area which is distanced from the overlapping area by a prescribed distance. In the case where an aperture of the collection optical system is a circle having a radius of 1, the overlapping area is an area where two circles overlap, the circles each having a radius of 1 and being centered around a point which is xcex/(NAxc2x7Gp) away, in a direction perpendicular to the track, from a center of the aperture, where xcex is the wavelength of the beam emitted by the light source, NA is the numerical aperture of the collection optical system, Gp is the distance between centers of two adjacent tracks of the information memory medium, and xcex/(NAxc2x7Gp) less than 1.
In one embodiment of the invention, the tracking error signal generator generates a tracking error signal using a signal obtained from the detection area which receives a beam in an area excluding the overlapping area, the beam being included in the reflected beam.
In one embodiment of the invention, the light division element includes at least two division lines which are substantially parallel to the tracks. The at least two division lines are arranged so as to sandwich the overlapping area of the reflected beam therebetween, and the tracking error signal generator generates a tracking error signal based on an operation of a signal obtained from the detection area which receives a beam incident on an area outside the at least two division lines, the beam being included in the reflected beam.
In one embodiment of the invention, the tracking error signal generator corrects a tracking error signal using a signal obtained from the detection area which receives a beam in the overlapping area and the vicinity thereof, the beam being included in the reflected beam.
In one embodiment of the invention, the light division element includes division lines in the number of N which are substantially parallel to the tangent to the tracks, wherein N is an odd integer of 3 or more. The two of the division lines are arranged so as to sandwich the overlapping area of the reflected beam therebetween. The remaining division lines are arranged between the two of the division lines. The tracking error signal generator generates a tracking error signal using signals obtained from the detection area which receives a beam incident on a first area and a second area which are outside the two of the division lines and exclude the overlapping area, the beam being included in the reflected beam. The tracking error signal generator further generates a correction signal by alternately inverting the polarity of signals obtained from the detection area which receives a beam incident on an even number of areas sandwiched between the two of the division lines, the beam being included in the reflected beam, and then adding together the signals obtained from the detection area. The tracking error signal generator then adds the tracking error signal and the correction signal or subtracts the correction signal from the tracking error signal.
In one embodiment of the invention, the light division element includes division lines in the number of N which are substantially parallel to the tangent to the tracks, wherein N is an odd integer of 3 or more. The two of the division lines are arranged so as to sandwich the overlapping area therebetween. The remaining division lines are arranged between the two of the division lines. The tracking error signal generator generates a correction signal by multiplying a value of each of the signals with a prescribed value, the signals being obtained from the detection area which receives a beam incident on an even number of areas sandwiched between the two of the division lines, the beam being included in the reflected beam, and then alternately inverting the polarity of the resultant signals, and adding together those signals. The tracking error signal generator then adds the tracking error signal and the correction signal or subtracts the correction signal from the tracking error signal.
In one embodiment of the invention, the light division element is a holographic element.
In one embodiment of the invention, the light division element is integral with a collection optical system.
In one embodiment of the invention, the light division element is a division line of the light detector.
According to still another aspect of the invention, an optical head device includes a light source for emitting at least one of a coherent beam and a quasi-monochromatic beam; a collection optical system for collecting the beam emitted by the light source to an information memory medium having at least one track, at least one mark and at least one space; a light detector having a plurality of detection areas for receiving the beam reflected by the information memory medium and outputting a signal in accordance with a light amount of the beam received; a tracking error signal generator for receiving the signals output from the light detector and generating a tracking error signal based on the signals; and a light reduction element provided on a beam path for reducing the light transmittance of the overlapping area and the vicinity thereof. In the case where an aperture of the collection optical system is a circle having a radius of 1, the overlapping area is an area where two circles overlap, the circles each having a radius of 1 and being centered around a point which is xcex/(NAxc2x7Gp) away, in a direction perpendicular to the track, from a center of the aperture, where xcex is the wavelength of the beam emitted by the light source, NA is the numerical aperture of the collection optical system, Gp is the distance between centers of two adjacent tracks of the information memory medium, and xcex/(NAxc2x7Gp) less than 1.
In one embodiment of the invention, the light reduction element is integral with the collection optical system.
In one embodiment of the invention, the light reduction element is a holographic element.
According to still another aspect of the invention, an optical head device includes a light source for emitting at least one of a coherent beam and a quasi-monochromatic beam; an optical element for receiving the beam emitted by the light source and dividing the beam into first beam and a second beam an effective numerical aperture of the collection optical system with respect to the first beam being different from an effective numerical aperture of the collection optical system with respect to the second beam; a collection optical system for receiving the first beam and the second beam and converging the first and second beams into a microscopic spot on an information memory medium; a beam branching element for receiving the beam diffracted and/or reflected by the information memory medium and branching the beam; a light detector for receiving the branched beam and outputting a signal in accordance with a light amount of the beam received; a signal processing section for receiving the signal from the light detector and performing an operation of the signal; a driving section for determining relative positions of the collection optical system and the information memory medium based on the signal output from the signal processing section; and a tracking error signal generator for generating a tracking error signal using the first or second beam with respect to which the effective numerical aperture of the collection optical system is smaller.
In one embodiment of the invention, the information memory medium includes marks or prescribed grooves for realizing detection of the tracking error signal, where Gp is the cycle of the marks or grooves, and NA is the numerical aperture of the collection optical system, the first beam has a wavelength xcex represented by Gp greater than xcex/NA, and the second beam has a wavelength xcex represented by Gp less than xcex/NA, and the tracking error signal generator generates a tracking error signal based on the second beam. In this specification, the cycle of the grooves refers to the distance between the center of one groove and the center of a groove adjacent thereto.
In one embodiment of the invention, an optical axis of the first beam is substantially coincident with an optical axis of the second beam.
In one embodiment of the invention, the optical element is a polarization filter.
In one embodiment of the invention, the optical element is integral with the collection optical system.
According to still another aspect of the invention, an inclination detection apparatus includes a light source for emitting at least one of a coherent beam and a quasi-monochromatic beam; a collection optical system for receiving the beam emitted by the light source and converging the beam into a microscopic spot on an information memory medium; a beam branching element for receiving the beam diffracted and/or reflected by the information memory medium and branching the beam; a light detector for receiving the branched beam and outputting a signal in accordance with a light amount of the beam received; a signal processing section for receiving the signal from the light detector and performing an operation of the signal; and a driving section for performing focusing control and tracking control to determine relative positions of the collection optical system and the information memory medium. The light detector includes a plurality of detection areas. The information memory medium has a first pattern area including a mark and a space and a second pattern area including prescribed grooves. The first pattern area and the second pattern area are alternately arranged on the information memory medium. The signal processing section detects an angle made by the beam collected by the collection optical system and the information memory medium, using a signal obtained by the light detector when one of the first pattern area and the second pattern area is irradiated by the beam collected by the collection optical system.
In one embodiment of the invention, in the case where the mark and the space in the first pattern area are irradiated by the beam collected by the collection optical system, tracking control is performed using the signal obtained by the light detector. In the case where the second pattern area is irradiated by the beam collected by the collection optical system, the angle made by the beam collected by the collection optical system and the information memory medium is detected using a signal obtained by the light detector.
In one embodiment of the invention, in the case where the second pattern area is irradiated by the beam collected by the collection optical system, tracking control is performed using the signal obtained by the light detector. In the case where the first pattern area as irradiated by the beam collected by the collection optical system, the angle made by the beam collected by the collection optical system and the information memory medium is detected using a signal obtained by the light detector.
In one embodiment of the invention, in the case where the mark and the space of the first pattern area are irradiated by the beam collected by the collection optical system, the angle made by the beam collected by the collection optical system and the information memory medium is detected using a signal obtained by the light detector.
In one embodiment of the invention, the inclination detection apparatus has the relationship of NA greater than xcex/Gp where Gp is the cycle of marks in the first pattern area or the cycle of the grooves in the second pattern area, xcex is the wavelength of the beam emitted by the light source, and NA is the numerical aperture of a part of the collection optical system facing the information memory medium.
According to still another aspect of the invention, an optical information processing apparatus includes a light source for emitting at least one of a coherent beam and a quasi-monochromatic beam; a collection optical system for receiving the beam emitted by the light source and converging the beam into a microscopic spot on an information memory medium; a beam branching element for receiving the beam diffracted and/or reflected by the information memory medium and branching the beam; a light detector for receiving the branched beam and outputting a signal in accordance with a light amount of the beam received; a signal processing section for receiving the signal from the light detector and performing an operation of the signal; a first driving section for performing focusing control and tracking control to determine relative positions of the collection optical system and the information memory medium; and a second driving section for changing the angle made by the beam collected by the collection optical system and the information memory medium. The light detector includes a plurality of detection areas. The information memory medium has patterns or prescribed grooves for generating a tracking error signal. NA greater than xcex/Gp where Gp is the cycle of patterns or grooves, xcex is the wavelength of the beam emitted by the light source, and NA is the numerical aperture of a part of the collection optical system facing the information memory medium.
According to still another aspect of the invention, an optical information pressing apparatus includes a light source for emitting at least one of a coherent beam and a quasi-monochromatic beam; a collection optical system for receiving the beam emitted by the light source and converging the beam into a microscopic spot on an information memory medium; a beam branching element for receiving the beam diffracted and/or reflected by the information memory medium and branching the beam; a light detector for receiving the branched beam and outputting a signal in accordance with a light amount of the beam received; a signal processing section for receiving the signal from the light detector and performing an operation of the signal; a first driving section for performing focusing control and tracking control to determine relative positions of the collection optical system and the information memory medium; and a second driving section for changing the angle made by the beam collected by the collection optical system and the information memory medium. The light detector includes a plurality of detection areas. The information memory medium has a first pattern area including a mark and a space and a second pattern area including prescribed grooves. The first pattern area and the second pattern area are alternately arranged on the information memory medium. The signal processing section detects an angle made by the beam collected by the collection optical system and the information memory medium, using a signal obtained by the light detector, and also generates a signal for driving the second driving section, when one of the first pattern area and the second pattern area is irradiated by the beam collected by the collection optical system.
In one embodiment of the invention, in the case where the mark in the first pattern area is irradiated by the beam collected by the collection optical system, tracking control is performed using the signal obtained by the light detector. In the case where the second pattern area is irradiated by the beam collected by the collection optical system, the angle made by the beam collected by the collection optical system and the information memory medium is detected using a signal obtained by the light detector.
In one embodiment of the invention, in the case where the second pattern area is irradiated by the beam collected by the collection optical system, tracking control is performed using the signal obtained by the light detector. In the case where the first pattern area is irradiated by the beam collected by the collection optical system, the angle made by the beam collected by the collection optical system and the information memory medium is detected using a signal obtained by the light detector.
In one embodiment of the invention, in the case where the mark and the space of the first pattern area are irradiated by the beam collected by the collection optical system, the angle made by the beam collected by the collection optical system and the information memory medium is detected using a signal obtained by the light detector.
In one embodiment of the invention, the optical information prossing apparatus has the relationship of NA greater than xcex/Gp where Gp is the cycle of marks in the first pattern area or the cycle of the grooves in the second pattern area, xcex is the wavelength of the beam emitted by the light source, and NA is the numerical aperture of a part of the collection optical system facing the information memory medium.
According to still another aspect of the invention, an optical head device includes a light source for emitting at least one of a coherent beam and a quasi-monochromatic beam; a collection optical system for collecting the beam emitted by the light source to an information memory medium having a track which has at least one mark and at least one space selectively arranged; alight detector for receiving the beam reflected by the information memory medium and outputting a signal in accordance with a light amount of the beam received; a light division element for dividing the beam reflected by the information memory medium so as to be received by the light detector; an information reproduction signal generator for generating an information reproduction signal for reproducing information stored in the track, based on a signal indicating the difference between the beans incident on a first area and a second area defined by a division line of the light division element; and a changing element for changing a region included in the first area, a region included in the second area, or a region included in both the first area and the second area in accordance with the positional relationship between the light collection point of the light from the collection optical system and the track.
In one embodiment of the invention, in the case where the beam has a substantially circular cross section having a radius of 1 on the light division element, the light division element is divided into three areas by a first division line which is substantially parallel to the tangent to the track and is distanced from the center of the substantially circular cross section by a prescribed distance d, and a second division line which is substantially parallel to the tangent to the track and is distanced from the center of the substantially circular cross section by the prescribed distance d in an opposite direction to the first division line; the area which is outside the first division line and thus excludes the center of the substantially circular cross section may be defined as area A, the area sandwiched by the first division line and the second division line may be defined as area B, and the area which is outside the second division line and thus excludes the center of the substantially circular cross section may be defined as area C. When the light collection point from the collection optical system is at a first position on the information memory medium which is distanced in one direction from the track by a prescribed distance, the information reproduction signal generator generates an information reproduction signal for reproducing information stored in the information memory medium, with the area A being the first area and a sum of the areas B and C being the second area. When the light collection point from the collection optical system is at a second position on the information memory medium which is distanced from the track by the prescribed distance in an opposite direction to the first position, the information reproduction signal generator generates an information reproduction signal for reproducing information stored in the track, with a sum of the areas A and B being the first area and the area C being the second area.
In one embodiment of the invention, where the beam has a substantially circular cross section having a radius of 1 on the light division element, the light division element is divided into four areas by a first division line which is substantially parallel to the tangent to the track and is distanced from the center of the substantially circular cross section by a prescribed distance d, a second division line which is substantially parallel to the tangent to the track and is distanced from the center of the substantially circular cross section by the prescribed distance d in an opposite direction to the first division line, and a third division line which is substantially parallel to the tangent to the track and runs through the center of the substantially circular cross section; the area which is outside the first division line and thus excludes the center of the substantially circular cross section may be defined as area A, the area sandwiched by the first division line and the third division line may be defined as area B, the area sandwiched by the third division line and the second division line may be defined as area C, and the area which is outside the second division line and thus excludes the center of the substantially circular cross section may be defined as area D. When the light collection point from the collection optical system is at a first position on the information memory medium which is distance, in one direction from the track by a prescribed distance, the information reproduction signal generator generates an information reproduction signal for reproducing information stored in the information memory medium, with the area A being the first area and the area C and D being the second area. When the light collection point from the collection optical system is at a second position on the information memory medium which is distanced from the track by the prescribed distance in an opposite direction to the first position, the information reproduction signal generator generates an information reproduction signal for reproducing information stored in the track, with the areas is A and B being the first area and the area D being the second area.
According to still another aspect of the invention, an optical head device includes a light source for emitting at least one of a coherent beam and a quasi-monochromatic beam; a collection optical system for collecting the beam emitted by the light source to an information memory medium having a track which has at least one mark and at least one space selectively arranged; a light detector having a plurality of detection areas for receiving the beam reflected by the information memory medium and outputting a signal in accordance with a light amount of the beam received; a light division element for dividing the beam reflected by the information memory medium so as to be received by the light detector; and an information reproduction signal generator for generating an information reproduction signal for reproducing information stored in the track, based on a signal indicating the difference between the beams incident on a first area and a second area defined by a division line of the light division element. In the case where the beam has a substantially circular cross section having a radius of 1 on the light division element, the light division element is divided into three areas by a first division line which is substantially parallel to the tangent to the track and is distanced from the center of the substantially circular cross section by a prescribed distance d, and a second division line which is substantially parallel to the tangent to the track and is distanced from the center of the substantially circular cross section by the prescribed distance d in an opposite direction to the first division line, one of the areas excluding the center of the substantially circular cross section may be defined as the first area, and another area excluding the center of the substantially circular cross section may be defined as the second area. When the light collection point from the collection optical system is at a position on the information memory medium which is distanced from the track by a prescribed distance, the information reproduction signal generator generates an information reproduction signal for reproducing information stored in the track.
According to still another aspect of the invention, an optical head device includes a light source for emitting one of a coherent beam or a quasi-monochromatic beam; a collection optical system for collecting the beam emitted by the light source to an information memory medium having a track which has at least one mark and at least one space selectively arranged; a light detector having a plurality of detection areas for receiving the beam reflected by the information memory medium and outputting a signal in accordance with a light amount of the beam received; a light division element for dividing the beam reflected by the information memory medium so as to be received by the light detector; and an information reproduction signal generator for generating an information reproduction signal for reproducing information stored in the track, based on a signal indicating the difference between the beams incident on a first area and a second area defined by a division line of the light division element. In the case where the beam has a substantially circular cross section having a radius of 1 on the light division element, the light division element is divided into four areas by a first division line which is substantially parallel to the tangent to the track and is distanced from the center of the substantially circular cross section by a prescribed distance d, a second division line which is substantially parallel to the tangent to the track and is distanced from the center of the substantially circular cross section by the prescribed distance d in an opposite direction to the first division line, and a third division line which is substantially parallel to the tangent to the track and runs through the center of the substantially circular cross section, a sum of the area which is outside the first division line and thus excludes the center of the substantially circular cross section and the area sandwiched by the third division line and the second division line may be defined as the first area, and a sum of the area sandwiched by the first division line and the third division line and the area which is outside the second division line and thus excludes the center of the substantially circular cross section may be defined as a second area. When the light collection point from the collection optical system is at a position on the information memory medium which is distanced from the track by a prescribed distance, the information reproduction signal generator generates an information reproduction signal for reproducing information stored in the track.
In one embodiment of the invention, in the case where the beam has a substantially circular cross section having a radius of 1 on the light division element, the distance d between the center of the substantially circular cross section and each of the first division line and the second division line is 0.1 or more and 0.3 or less.
According to still another aspect of the invention, an optical head device includes a light source for emitting at least one of a coherent beam and a quasi-monochromatic beam; a collection optical system for collecting the beam emitted by the light source to an information memory medium having tracks having a mark and a space selectively arranged or tracks having prescribed grooves; a light detector having a plurality of detection areas for receiving the beam reflected by the information memory medium and outputting a signal in accordance with a light amount of the beam received a tracking error signal generator for receiving the signals from the light detector and generating a tracking error signal based on the signals received; and a light division element for dividing the beam reflected by the information memory medium so as to be received by the light detector. Where xcex is the wavelength of the beam emitted by the light source, NA is the numerical aperture of the collection optical system, Gp is the distance between centers of two adjacent tracks of the information memory medium, xcex/(NAxc2x7Gp)xe2x89xa71, and the beam has a substantially circular cross section having a radius of 1 on the light division element. The light division element has at least five division lines which are substantially parallel to the tangent to the tracks. Where the division line running through the center of the substantially circular cross section is a first division line, two division lines which are distanced from the first division line by a distance of about 0.1 in two opposite directions are a second division line and a third division line, and two division lines which are distanced from two ends of the cross section by a distance of about 0.1 are a fourth division line and a fifth division line. The tracking error signal generator generates the tracking error signal by alternately inverting the polarity of the signals obtained in accordance with the beams incident on six areas defined by the five division lines and adding together those signals.
According to still another aspect of the invention, an optical head device includes a light source for emitting at least one of a coherent beam and a quasi-monochromatic beam; a collection optical system for collecting the beam emitted by the light source to an information memory medium having tracks having a mark and a space selectively arranged or tracks having prescribed grooves; a light detector having a plurality of detection areas for receiving the beam reflected by the information memory medium and outputting a signal in accordance with a light amount of the beam received; a tracking error signal generator for receiving the signals from the light detector and generating a tracking error signal based on the signals received; and a light division element for dividing the beam reflected by the information memory medium so as to be received by the light detector. Where xcex is the wavelength of the beam emitted by the light source, NA is the numerical aperture of the collection optical system, Gp is the distance between centers of two adjacent tracks of the information memory medium, xcex/(NAxc2x7Gp)xe2x89xa71, and an aperture of the collection optical system is a circle having a radius of 1. The light division element has division lines in the number of N which are substantially parallel to the tangent to the tracks, where N is an odd integer of 3 or more. The two of the division lines are positioned within a width of about 0.6 from the center of the aperture of the collection optical system. The remaining division lines are positioned between the two division lines at an equal interval. The tracking error signal generator generates the tracking error signal using signals obtained from the areas which are outside the two division lines and thus exclude the center of the substantially circular cross section. The tracking error signal generator generates a correction signal by alternately inverting the polarity of signals obtained from an even number of areas sandwiched by the two division lines and adding together those signals. The tracking error signal generator adds the tracking error signal and the correction signal or subtracts the correction signal from the tracking error signal.
In one embodiment of the invention, the line division element is a diffraction element.
In one embodiment of the invention, the line division element is a division line of the light detector.
According to still another aspect of the invention, an optical head device includes a light source for emitting at least one of a coherent beam and a quasi-monochromatic beam; a collection optical system for collecting the beam emitted by the light source to an information memory medium having tracks having a mark and a space selectively arranged or tracks having prescribed grooves; a diffraction element for receiving a beam diffracted by the information memory medium and generating a diffraction beam; and a light detector having a plurality of detection areas for receiving the beam diffracted by the diffraction element and outputting a signal in accordance with a light amount of the beam received. The diffraction element includes a plurality of areas. A diffraction beam of a desired order generated by an area group A included in the plurality of areas form a first spherical wave. A diffraction beam of a desired order generated by an area group B included in the plurality of areas but excluded from the area group A form a second spherical wave, which has a light collection point farther than the light collection point of the first spherical wave with respect to the diffraction element. A focusing error signal generator is provided for generating a focusing error signal based on the difference between the cross sections of the first spherical wave and the second spherical wave on the light detector. The diffraction element has at least one division line perpendicular to the tangent to the tracks. Either one of portions sandwiching the at least one division line is included in the area group A and the other portion is included in the area group B.
According to still another aspect of the invention, an optical head device includes a light source for emitting at least one of a coherent beam and a quasi-monochromatic beam; a collection optical system for collecting the beam emitted by the light source to an information memory medium having tracks having a mark and a space selectively arranged or tracks having prescribed grooves; a diffraction element for receiving a beam diffracted by the information memory medium and generating a diffraction beam; and a light detector having a plurality of detection areas for receiving the beam diffracted by the diffraction element and outputting a signal in accordance with a light amount of the beam received. The diffraction element includes a plurality of areas. A diffraction beam of a desired order generated by an area group A included in the plurality of areas form a first spherical wave. A diffraction beam of a desired order generated by an area group B included in the plurality of areas but excluded from the area group A form a second spherical wave, which has a light collection point farther than the light collection point of the first spherical wave with respect to the diffraction element. A focusing error signal generator is provided for generating a focusing error signal based on the difference between the cross sections of the first spherical wave and the second spherical wave on the light detector. The diffraction element has a diffraction area which is larger than the area corresponding to an aperture of the collection optical system. The diffraction element has a first division line and a second division line interposing the aperture, the first division line and the second division line being parallel to the tangent to the tracks and in contact with an outer periphery of the aperture. Either one of portions sandwiching the first division line or the second division line is included in the area group A and the other portion is included in the area group B.
In one embodiment of the invention, the diffraction element is integral with the collection optical system.
According to still another aspect of the invention, a method for processing optical information includes the steps of emitting at least one of a coherent beam and a quasi-monochromatic beam; collecting the beam emitted by the light source to an information memory medium having at least one track, at least one mark and at least one space; receiving the beam reflected by the information memory medium by a plurality of detection areas and outputting a signal in accordance with a light amount of the beam received; and receiving the signals output from the plurality of detection areas and generating a tracking error signal based on the signals. The step of generating a tracking error signal includes the step of subtracting a component of the signal obtained from an overlapping area from the tracking error signal. In the case where an aperture of a collection optical system for collecting the beam is a circle having a radius of 1, the overlapping area is an area where two circles overlap, the circles each having a radius of 1 and being centered around a point which is xcex/(NAxc2x7Gp) away, in a direction perpendicular to the track, from a center of the aperture of the collection optical system, and where xcex is the wavelength of the emitted beam, NA is the numerical aperture of the collection optical system, and Gp is the distance between centers of two adjacent tracks of the information memory medium, xcex/(NAxc2x7Gp) less than 1.
According to still another aspect of the invention, a method for processing optical information includes the steps of emitting at least one of a coherent beam and a quasi-monochromatic beam; receiving the beam emitted by the light source and dividing the beam into a first beam and a second beam; receiving the first beam and the second beam and collecting the first beam and the second beam into a microscopic spot on an information memory medium, an effective numerical aperture of the collection optical system for collecting the beams with respect to the first beam being different from an effective numerical aperture of the collection optical system with respect to the second beam; receiving the beam diffracted and/or reflected by the information memory medium and branching the beams receiving the branched beam and outputting a signal in accordance with a light amount of the beam received; receiving the output signal and performing an operation of the signal; determining relative positions of the collection optical system and the information memory medium based on the signal obtained as a result of the operation; and generating a tracking error signal using the first or second beam with respect to which the effective numerical aperture of the collection optical system is smaller.
According to still another aspect of the invention, a method for processing optical information includes the steps of emitting at least one of a coherent beam and a quasi-monochromatic beam; receiving the beam emitted by the light source and converging the beam into a microscopic spot on an information memory medium; receiving the beam diffracted and/or reflected by the information memory medium and branching the beam; receiving the branched beam by a plurality of detection areas and outputting a signal in accordance with a light amount of the beam received; receiving the output signal and performing an operation of the signal; performing focusing control and tracking control to determine relative positions of a collection optical system for converging the beam and the information memory medium; and changing the angle made by the beam converged by the collection optical system and the information memory medium. The information memory medium has patterns or prescribed grooves for generating a tracking error signal, and NA greater than xcex/Gp where Gp is the cycle of the patterns or grooves, xcex is the wavelength of the emitted beam, and NA is the numerical aperture of a part of the converging system facing the information memory medium.
According to still another aspect of the invention, a method for processing optical information includes the steps of emitting at least one of a coherent beam and a quasi-monochromatic beam; collecting the beam emitted by the light source to an information memory medium having a track having a mark and a space selectively arranged; receiving the beam reflected by the information memory medium by a plurality of detection areas and outputting a signal in accordance with a light amount of the beam received; dividing the light reflected by the information memory medium; generating an information reproduction signal for reproducing information stored in the track based on a signal indicating the difference between a signal obtained in accordance with the beams incident on a first area and a second area obtained as a result of dividing the light; and changing a region included in the first area, a region included in the second area, or a region included in both the first area and the second area, in accordance with the positional relationship between the light collection point of the light from a collection optical system for collecting the beam and the track.
According to still another aspect of the invention, a method for processing optical information includes the steps of emitting at least one of a coherent beam and a quasi-monochromatic beam; collecting the beam emitted by the light source to an information memory medium having tracks having a mark and a space selectively arranged or tracks having prescribed grooves; receiving the beam reflected by the information memory medium by a detection area and outputting a signal in accordance with a light amount of the beam received; receiving the output signal and generating a tracking error signal based on the signal received; and dividing the light reflected by the information memory medium. Where xcex is the wavelength of the emitted beam, NA is the numerical aperture of a collection optical system for collecting the beam, Gp is the distance between centers of two adjacent tracks of the information memory medium, xcex/(NAxc2x7Gp)xe2x89xa71, and the beam has a substantially circular cross section having a radius of 1, the light division element has at least five division lines which are substantially parallel to the tangent to the tracks: the division line running through the center of the substantially circular cross section may be defined as a first division line, two division lines which are distanced from the first division line by a distance of about 0.1 in two opposite directions may be defined as a second division line and a third division line, and two division lines which are distanced from two ends of the cross section by a distance of about 0.1 may be defined as a fourth division line and a fifth division line. The method further includes the step of generating the tracking error signal by alternately inverting the polarity of the signals obtained in accordance with the beams incident on six areas defined by the five division lines and adding together those signals.
According to still another aspect of the invention, a method for processing optical information includes the steps of emitting at least one of a coherent beam and a quasi-monochromatic beam; collecting the beam emitted by the light source to an information memory medium having tracks having a mark and a space selectively arranged or tracks having prescribed grooves; receiving the beam reflected by the information memory medium by a plurality of areas and generating a diffraction beam; receiving the diffracted beam by a plurality of detection areas and outputting a signal in accordance with a light amount of the beam received; and generating a focusing error signal based on the difference between the size of the cross section of a first spherical wave and the size of the cross section of a second spherical waves. The first spherical wave corresponds to a diffraction beam of a desired order generated by an area group A included in the plurality of areas. The second spherical wave corresponds to a diffraction beam of a desired order generated by an area group B included in the plurality of areas but excluded from the area group A. Either one of portions sandwiching the at least one division line is included in the area group A and the other portion is included in the area group B.
Thus, the invention described herein makes possible the advantages of (1) providing an optical head device having stable servo characteristic is and thus realizes stable formation of marks at appropriate positions on or in the vicinity of the tracks for information recording, and also realizes correct information reproduction and stable information recording and erasure with a sufficiently low error ratio; (2) providing an inclination detection apparatus for detecting an inclination of 0.5 degrees or less with high precision; and (3) an optical information processing apparatus for realizing stable information recording to and reproduction from an information memory medium which is significantly curved.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.